Alternative Support Systems for Cantilever - National Transportation ...

EXECUTIVE SUMMARY
During the 2004 hurricane season, the failure of several foundations of cantilever sign structures
occurred along Florida highways. Those failures necessitated a review of the design and
construction procedures for the foundations of cantilever sign structures. The failures were
determined to be caused by concrete breakout of the anchors subjected to shear parallel to the
edge caused by torsional loading. The research team tested a retrofit option using carbon fiber-
reinforced polymer (CFRP) wrap and design guidelines for determining the susceptibility of
failure for current systems and design of the CFRP wrap retrofit design were created. Having
found the failure mechanism, alternative support structures were recommended for future
research, which became the basis for the current project.
The primary objectives of this research program were as follows:
• Identify a viable alternative to transfer load from the superstructure to the foundation other
than through anchor bolts.
• Provide design guidelines for the alternative selected.
In order to complete these objectives, a literature review and experimental program were
conducted. The findings of the literature review were used to develop the experimental program.
The literature review and the results of the experimental program were used to develop the
design guidelines for the alternative selected. In addition to the primary objectives, alternative
connections were also identified for consideration for future testing.
After a literature review and exploration of other industries’ options, an embedded pipe and plate
section was selected as a viable alternative. The clear load path and ability to handle both
torsional and flexural load made the embedded pipe and plate section the most ideal alternative.
Testing proved that the embedded pipe and plate section was able to transfer the torsional and
flexural load to the concrete satisfactorily. Testing also proved that American Concrete Institute
(ACI) 318 code equations for concrete breakout from applied shear could be modified to
accurately predict the concrete breakout strength of the embedded pipe and plate section.
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